As of 4:45 p.m. Tuesday, more than 2,500 Windsor-Essex residents were without power. The affected area is southwest of Windsor, covering a large part of the county including Maidstone, Essex, Cottam and Woodslee.
Hydro One says the reason for the outage is still unknown as crews work to assess the interruption.
It was first reported just before 4 p.m.
At last check Hydro One's hope was to have power fully restored by around 7 p.m.